decode takes a dynamic decoder

5 files changed, 46 insertions, 36 deletions

diff --git a/README.md b/README.md
index 9a0c9fc..8e6a35a 100644
--- a/README.md
+++ b/README.md
@@ -23,9 +23,9 @@ import gleam/json.{object, string, list, int, null}
 pub fn cat_to_json(cat: Cat) -> String {
   object([
     #("name", string(cat.name)),
-    #("lives", int(9),
+    #("lives", int(cat.lives),
     #("flaws", null()),
-    #("nicknames", array(["Kitty", "Sweetie"], of: string)),
+    #("nicknames", array(cat.nicknames, of: string)),
   ])
   |> json.to_string
 }
@@ -39,27 +39,17 @@ JSON is decoded into a `Dynamic` value which can be decoded using the
 ```rust
 import myapp.{Cat}
 import gleam/json
-import gleam/dynamic
+import gleam/dynamic.{field, list, int, string}
 import gleam/result
 
-pub fn cat_from_json(json: String) -> Result<Cat, MyError> {
-  try data = 
-    json.decode(encoded)
-    |> result.map_error(InvalidJson)
+pub fn cat_from_json(json_string: String) -> Result<Cat, json.DecodeError> {
+  let cat_decoder = dynamic.decode2(
+    Cat,
+    field("name", of: string),
+    field("lives", of: int),
+    field("nicknames", of: list(string)),
+  )
 
-  let data = dynamic.from(data)
-  try cat = {
-    try name = dynamic.field(data, "name")
-    try name = dynamic.string(name)
-    Ok(Cat(name))
-  }
-  |> result.map_error(InvalidFormat)
-
-  Ok(cat)
-}
-
-pub type MyError {
-  InvalidJson(json.DecodeError)
-  InvalidFormat(dynamic.DecodeError)
+  json.decode(from: json_string, using: cat_decoder)
 }
 ```
diff --git a/gleam.toml b/gleam.toml
index a471dd0..609237b 100644
--- a/gleam.toml
+++ b/gleam.toml
@@ -3,8 +3,6 @@ version = "0.2.0"
 licences = ["Apache-2.0"]
 description = "Work with JSON in Gleam"
 
-# target = "javascript"
-
 repository = { type = "github", user = "gleam", repo = "json" }
 links = [
   { title = "Website", href = "https://gleam.run" },
@@ -12,7 +10,7 @@ links = [
 ]
 
 [dependencies]
-gleam_stdlib = "~> 0.18"
+gleam_stdlib = "~> 0.19"
 thoas = "~> 0.2"
 
 [dev-dependencies]
diff --git a/manifest.toml b/manifest.toml
index d71063c..a406eb6 100644
--- a/manifest.toml
+++ b/manifest.toml
@@ -2,12 +2,12 @@
 # You typically do not need to edit this file
 
 packages = [
-  { name = "gleam_stdlib", version = "0.18.1", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "763ECD87D54D08755EE4C8551720D122FDCA47F61D1CA8AF23B19A90395A7468" },
-  { name = "gleeunit", version = "0.5.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "F7FA7477D930178C1E59519DBDB5E086BE3A6B65F015B67DA94D30A323062154" },
+  { name = "gleam_stdlib", version = "0.19.2", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "FFA79EA12369F122B68885E694E097D6810402A2F86BFF48AAE9E40ACE654F4C" },
+  { name = "gleeunit", version = "0.6.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "77701A5E5A565727E1EEAC9196FB878D544049B6331CD0305B5A69699135EA1C" },
   { name = "thoas", version = "0.2.0", build_tools = ["rebar3"], requirements = [], otp_app = "thoas", source = "hex", outer_checksum = "630AAEE57FB3FDE201578E787259E15E788A27733D49DE8DCCE1354DB1885B8D" },
 ]
 
 [requirements]
-gleam_stdlib = "~> 0.18"
+gleam_stdlib = "~> 0.19"
 gleeunit = "~> 0.5"
 thoas = "~> 0.2"
diff --git a/src/gleam/json.gleam b/src/gleam/json.gleam
index 7db916d..b94a1d4 100644
--- a/src/gleam/json.gleam
+++ b/src/gleam/json.gleam
@@ -11,6 +11,7 @@ pub type DecodeError {
   UnexpectedEndOfInput
   UnexpectedByte(byte: String, position: Int)
   UnexpectedSequence(byte: String, position: Int)
+  UnexpectedFormat(List(dynamic.DecodeError))
 }
 
 /// Decode a JSON string into dynamically typed data which can be decoded into
@@ -19,16 +20,31 @@ pub type DecodeError {
 /// ## Examples
 ///
 /// ```gleam
-/// > decode("[1,2,3]")
-/// Ok(dynamic.from([1, 2, 3]))
+/// > decode("[1,2,3]", dynamic.list(of: dynamic.int))
+/// Ok([1, 2, 3])
 /// ```
 ///
 /// ```gleam
-/// > decode("[")
+/// > decode("[", into: dynamic.list(of: dynamic.int))
 /// Error(UnexpectedEndOfInput)
 /// ```
 ///
-pub external fn decode(String) -> Result(Dynamic, DecodeError) =
+/// ```gleam
+/// > decode("1", into: dynamic.string)
+/// Error(UnexpectedFormat([dynamic.DecodeError("String", "Int", [])]))
+/// ```
+///
+pub fn decode(
+  from json: String,
+  using decoder: dynamic.Decoder(t),
+) -> Result(t, DecodeError) {
+  try dynamic_value = decode_to_dynamic(json)
+  dynamic_value
+  |> decoder
+  |> result.map_error(UnexpectedFormat)
+}
+
+external fn decode_to_dynamic(String) -> Result(Dynamic, DecodeError) =
   "gleam_json_ffi" "decode"
 
 /// Convert a JSON value into a string.
diff --git a/test/gleam_json_test.gleam b/test/gleam_json_test.gleam
index 7e93ab7..fb55c90 100644
--- a/test/gleam_json_test.gleam
+++ b/test/gleam_json_test.gleam
@@ -11,21 +11,27 @@ pub fn main() {
 }
 
 pub fn decode_test() {
-  json.decode("5")
-  |> result.map(dynamic.from)
-  |> should.equal(Ok(dynamic.from(5)))
+  json.decode(from: "5", using: dynamic.int)
+  |> should.equal(Ok(5))
 }
 
 pub fn decode_empty_test() {
-  json.decode("")
+  json.decode(from: "", using: dynamic.int)
   |> should.equal(Error(json.UnexpectedEndOfInput))
 }
 
 pub fn decode_unexpected_byte_test() {
-  json.decode("[}")
+  json.decode(from: "[}", using: dynamic.int)
   |> should.equal(Error(json.UnexpectedByte("0x7D", 1)))
 }
 
+pub fn decode_unexpected_format_test() {
+  json.decode(from: "[]", using: dynamic.int)
+  |> should.equal(Error(json.UnexpectedFormat([
+    dynamic.DecodeError(expected: "Int", found: "List", path: []),
+  ])))
+}
+
 pub fn encode_string_test() {
   json.string("hello")
   |> should_encode("\"hello\"")